Ultrahigh-resolution Mass Spectra Research Articles

Development of a Gaussian-Based Alignment Algorithm for the Ultrahigh-Resolution Mass Spectra of Dissolved Organic Matter

The alignment of ultrahigh-resolution mass spectra (UHR-MS) is critical to inspect the presence of unique and common peaks across multiple UHR-MS spectra. However, few attempts have been conducted to develop an automated alignment method. In this study, a novel automated alignment algorithm, namely, FTMSCombine, that follows a Gaussian distribution of mass errors was developed and then integrated with existing FTMSCalibrate and TRFu algorithms to establish an open-source analysis platform, namely, FTMSAnalysis, for the UHR-MS analysis of the dissolved organic matter. The developed FTMSCombine was capable of automatically aligning peaks across different UHR-MS spectra by averaging the m/z values of each peak cluster, although the alignment should be restricted to Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) spectra collected by instruments under similar conditions. The FTMSCombine exhibited an insignificant difference in the reproducibility of chemical formulae but significantly higher mass accuracy than the ICBM-OCEAN. In addition to improving the overall mass accuracy of the whole UHR-MS dataset, the FTMSCombine could effectively exclude scatters or noise peaks using an optional rule that restricts peaks (continuously) detected in at least a certain number of spectra in the UHR-MS spectra dataset. The successfully established FTMSAnalysis (freely available in the Supporting Information of this study) is of great potential in automatically analyzing UHR-MS spectra for dissolved organic matter (DOM) and will largely facilitate the elucidation of DOM chemodivesity by UHR-MS techniques including FTICR-MS.

Photochemical behavior of constructed wetlands-derived dissolved organic matter and its effects on Bisphenol A photodegradation in secondary treated wastewater

Free water surface flow (FWS) constructed wetlands (CWs) have been broadly applied for polishing secondary treated effluents. Dissolved organic matter derived from FWS CWs (WDOM) plays key roles in contaminants transformations. Conversely, photodegradation could shape the quantity and quality of WDOM, thereby affecting its roles in the photolysis of organic micropollutants (OMPs). Nevertheless, whether and how solar irradiation-induced photodegradation modify the properties of WDOM, and the effects of WDOM on the photodegradation of OMPs remain unclear. This study elucidates the photochemical behavior of two WDOM isolated from field-scale FWS CWs for effluent polishing under simulated sunlight irradiation using spectroscopic tools and high-resolution mass spectra. Furthermore, the roles of WDOM in the photodegradation of Bisphenol A (BPA), as a representative endocrine-disrupting compound (EDC), were comprehensively investigated. Solar irradiation was demonstrated to lower the molecular weight and aromaticity of WDOM, as well as weaken its light absorption. Ultrahigh-resolution mass spectra further confirmed that aromatic and unsaturated structures were susceptible to solar irradiation-induced photodegradation reactions. Subsequently, less aromatic and more saturated structures eventually formed under sunlight irradiation, consistent with the result from spectroscopic characterization. The reactive species produced from WDOM significantly enhanced the photodegradation of BPA with the kobs noticeably increasing 4-fold compared with the kobs for direct photolysis. Additionally, 3WDOM* was identified as the dominant reactive species leading to the photolysis of BPA in the presence of WDOM. These findings improve understanding of the phototransformation behavior of WDOM under sunlight irradiation and the roles that WDOM plays in the photochemical fate of coexisting OMPs in CWs treatment systems.

Assessment of artificial neural network to identify compositional differences in ultrahigh-resolution mass spectra acquired from coal mine affected soils

This study assessed the applicability of artificial neural networks (ANNs) as a tool to identify compounds contributing to compositional differences in coal-contaminated soils. An artificial neural network model was constructed from laser desorption ionization ultrahigh-resolution mass spectra obtained from coal contaminated soils. A good correlation (R2 = 1.00 for model and R2 = 0.99 for test) was observed between the measured and predicted values, thus validating the constructed model. To identify chemicals contributing to the coal contents of the soils, the weight values of the constructed model were evaluated. Condensed hydrocarbon and low oxygen containing compounds were found to have larger weight values and hence they were the main contributors to the coal contents of soils. In contrast, compounds identified as lignin did not contribute to the coal contents of soils. These findings were consistent with the conventional knowledge on coal and results from the conventional partial least square method. Therefore, we concluded that the weight interpretation following ANN analysis presented herein can be used to identify compounds that contribute to the compositional differences of natural organic matter (NOM) samples.

MFAssignR: Molecular formula assignment software for ultrahigh resolution mass spectrometry analysis of environmental complex mixtures

Ultrahigh resolution mass spectrometry is widely used for nontargeted analysis of complex environmental and biological mixtures, such as dissolved organic matter, due to its unparalleled ability to provide accurate mass measurements. Accurate and efficient characterization of these mixtures is critical to being better able to evaluate their effect on human health and climate. This characterization requires accurate mass signals free from isobaric interferences, instrument noise, and mass measurement biases, allowing for molecular formula identification. To address this need, an open source post-processing pipeline for ultrahigh resolution mass spectra of environmental complex mixtures software was developed. MFAssignR contains functions that perform noise estimation, 13C and 34S polyisotopic mass filtering, mass measurement recalibration, and molecular formula assignment as part of a consistent data processing environment. Novel applications of mass defect analysis were used in the functions for noise estimation and isotope pair identification. Using formula extensions, exact mass measurements are converted to unambiguous molecular formulas via data dependent pathways, reducing a priori decisions. Optional molecular formula ambiguity and multiple non-oxygen heteroatoms are provided for custom user applications, including isotopically labeled reactive species, halogen-containing species, or tandem ultrahigh resolution mass spectrometry. This represents uncommon flexibility for an open-source software package. To evaluate the performance of MFAssignR, it was used to characterize a sample of biomass burning influenced organic aerosol and the results were compared to those from other available methods of molecular formula assignment and noise estimation. The differences between the methods are described here. Overall, the inclusion of a full pipeline of data preparation functions and the data-dependent ambiguity reductions in MFAssignR render excellent results and make MFAssignR well-suited for the consistent and efficient analysis of environmental complex mixtures. MFAssignR is publicly available via GitHub.

Development and comparison of formula assignment algorithms for ultrahigh-resolution mass spectra of natural organic matter

Increasing number of application of ultrahigh-resolution mass spectrometry (UHR-MS) to natural organic matter (NOM) characterization requires an efficient and accurate formula assignment from a number of mass data. Herein, we newly developed two automated batch codes (namely TRFu and FuJHA) and assessed their formula assignment accuracy together with frequently used open access algorithms (i.e., Formularity and WHOI). Overall assignment accuracy for 8719 NOM-like emerging chemicals with known molecular formulae (mass range from 68 Da to 1000 Da) was highest (94%) for TRFu. Further, TRFu showed up to 99.1% formula assignment ratio for a total 76,880 UHR-MS peaks from 35 types of NOM (e.g., aquatic, soil/sediment, biochar). Therefore, as a reliable and practically feasible tool, the automated batch TRFu (freely available at ChemRxiv, https://doi.org/10.26434/chemrxiv.9917399) can precisely characterize UHR-MS spectra of various NOM and could be extended to non-target screening of NOM-like emerging chemicals in natural and engineered environments.

Determining the orientation of the flexural modes of a thermally driven microwire cantilever

Mechanical resonators are excellent transducers for ultrasensitive detection applications. Recent advances such as vectorial force sensing and ultrahigh-resolution mass spectra rely on the identification of two flexural vibrational modes of a resonator. The orientations of the flexural modes with respect to the incident optical axis are crucial parameters for a cantilevered resonator. Previous methods have adopted complex experimental setups using quadrant photodetectors or have required simultaneous detection of two flexural modes of the cantilever. In this paper, we propose a method for determination of the orientations of the flexural vibrations of a cantilever using a microlens optical fiber interferometer that takes both the light interference and the lateral light scattering of the cantilever into account. We demonstrated the method by experimentally determining the orientation of the first three flexural vibrational modes of a thermally driven microwire. Our method can be used to characterize individual flexural modes with arbitrary orientations and thus provides a new tool for detecting vectorial forces.

Yellowstone Hot Springs are Organic Chemodiversity Hot Spots

Yellowstone National Park hydrothermal springs were investigated according to their organic geochemistry with a special focus on the Yellowstone hot spring dissolved organic matter (YDOM) that was solid-phase extracted. Here we show that YDOM has a unique chemodiversity that has not yet been observed anywhere else in aquatic surface environments and that Yellowstone hot springs are organic chemodiversity hot spots. Four main geochemically classified hot spring types (alkaline-chloride, mixed alkaline-chloride, acid-chloride-sulfate and travertine-precipitating) exhibited distinct organic molecular signatures that correlated remarkably well with the known inorganic geochemistry and manifested themselves in excitation emission matrix fluorescence, nuclear magnetic resonance, and ultrahigh resolution mass spectra. YDOM contained thousands of molecular formulas unique to Yellowstone of which 80% contained sulfur, even in low hydrogen sulfide containing alkaline-chloride springs. This unique YDOM reflects the extreme organic geochemistry present in the hydrothermal features of Yellowstone National Park.

Formularity: Software for Automated Formula Assignment of Natural and Other Organic Matter from Ultrahigh-Resolution Mass Spectra.

Ultrahigh resolution mass spectrometry, such as Fourier transform ion cyclotron resonance mass spectrometry (FT ICR MS), can resolve thousands of molecular ions in complex organic matrices. A Compound Identification Algorithm (CIA) was previously developed for automated elemental formula assignment for natural organic matter (NOM). In this work, we describe software Formularity with a user-friendly interface for CIA function and newly developed search function Isotopic Pattern Algorithm (IPA). While CIA assigns elemental formulas for compounds containing C, H, O, N, S, and P, IPA is capable of assigning formulas for compounds containing other elements. We used halogenated organic compounds (HOC), a chemical class that is ubiquitous in nature as well as anthropogenic systems, as an example to demonstrate the capability of Formularity with IPA. A HOC standard mix was used to evaluate the identification confidence of IPA. Tap water and HOC spike in Suwannee River NOM were used to assess HOC identification in complex environmental samples. Strategies for reconciliation of CIA and IPA assignments were discussed. Software and sample databases with documentation are freely available.

An ultrahigh-resolution mass spectrometry study of ozonation products of petroleum sulfur compounds

Potential use of ultrahigh-resolution mass spectrometry for determination of sulfur-containing components of petroleum before and after ozonation has been described. The chemical composition of the petroleum before and after ozonation has been determined using a Fourier transform ion-cyclotron mass spectrometer with soft ionization techniques: atmospheric-pressure photoionization and positive- or negative-ion electrospray ionization. The article presents the main trends of change in the composition of petroleum sulfur components in the ozonation process as revealed on the basis of ultrahigh-resolution mass spectra.

Deuterium–hydrogen exchange reactions in peptides and polyatomic organic compounds, as studied on an ion cyclotron resonance mass spectrometer equipped with an ion trap with dynamic harmonization

The ultrahigh-resolution mass spectra of a substance P peptide labeled with deuterium have been obtained. The use of an ion trap with dynamic harmonization has made it possible to resolve the hyperfine isotopic structure of peaks and to reliably distinguish the hydrogen isotopes from the isotopes of carbon in the composition of the test molecules. The deuterium–hydrogen exchange reaction of humic acids has been performed in a gas phase, and it has been shown that the resolving power attained is sufficient for reliable interpretation of the results.

Selectivity of solid phase extraction of freshwater dissolved organic matter and its effect on ultrahigh resolution mass spectra.

Solid phase extraction (SPE) is often used for enrichment and clean-up prior to analysis of dissolved organic matter (DOM) by electrospray ionization (ESI) coupled to ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). It is generally accepted that extraction by SPE is not quantitative with respect to carbon concentration. However, little information is available on the selectivity of different SPE sorbents and the resulting effect for the acquired DOM mass spectra. Freshwater samples were extracted by the widely used PPL, HLB and C18 sorbents and the molecular composition and size distribution of the DOM in the extracts and in the permeates was compared to the original sample. Dissolved organic carbon (DOC) recoveries ranged between 20% and 65% for the three tested SPE sorbents. Size-exclusion chromatography coupled to organic carbon detection (SEC-OCD) revealed that limited recovery by PPL and HLB was primarily due to incomplete elution of a fraction of apparent high molecular weight from the solid phase. In contrast, incomplete retention on the solid phase, mainly observed for the C18 cartridge, was attributed to a fraction of low molecular weight. The FT-ICR mass spectra of the original sample and the SPE extracts did not differ significantly in their molecular weight distribution, but they showed sorbent specific differences in the degree of oxygenation and saturation. We concluded that the selective enrichment of freshwater DOM by SPE is less critical for subsequent FT-ICR MS analysis, because those fractions that are not sufficiently recovered have comparatively small effects on the mass spectra. This was confirmed by the extraction of model compounds, showing that very polar and small molecules are poorly extracted, but also have a low response in ESI-MS. Of the three tested SPE cartridges the PPL material offered the best properties for DOM enrichment for subsequent FT-ICR MS analysis as it minimizes too strong and too weak DOM-sorbent interactions.

MALDI and LDI Imaging of Forensic Samples by Using A Spiral-Trajectory Ion Optics Time-of-Flight Mass Spectrometer

Recently, matrix-assisted laser desorption/ionization (MALDI) imaging techniques have been developed for biological sciences to evaluate and understand the distribution of various chemicals on biological surfaces. In particular, this technique provides useful visual information about the locations of specific chemicals on surfaces. In this work, we explored the use of MALDI imaging for forensically relevant samples that included gunshot residue (GSR), fingerprints and ballpoint ink. These measurements were done using a spiraltrajectory ion optics time-of-flight mass spectrometer (SpiralTOF-MS [1]). This TOF system has a unique 17m flight path that provides ultrahigh-resolution mass spectra over a wide m/z range, even if the sample is not perfectly flat. Additionally, the m/z axis is very stable over the long measurement times required for MALDI imaging. GSR samples were obtained on an electrically conductive adhesive that was pressed against the back of a shooter’s hand after a handgun was discharged. The fingerprint samples were collected on electrically conductive ITO glass slides from both a smoker and a non-smoker. The smoker’s fingerprint was collected immediately after smoking a cigarette. 2,5-dihydroxybenzoic acid (DHB) was used as the MALDI matrix. This matrix was dissolved in methanol at a fixed concentration of 30 mg/mL. 1-2 mL of DHB solution was sprayed on each sample surface by using a commercial airbrush. Samples were then analyzed by using a high-resolution MALDI-TOFMS instrument. A polypropylene glycol (PPG) mixture of average MW 425 and 1000 were used as an external exact-mass reference standard. The GSR sample surface was analyzed for inorganic element distributions. As a starting point, we

Detection, identification, and quantification of hydroxylated bis(2-ethylhexyl)-tetrabromophthalate isomers in house dust.

Ultra-High Resolution LC/mass spectrometry (LC-UHRMS; Thermo Fisher Q-Exactive) was used to identify two novel isomers of hydroxylated bis(2-ethylhexyl)-tetrabromophthalate (OH-TBPH) which were unexpectedly observed in a commercial standard of TBPH. By combining ultra-high resolution (UHR) mass spectra (MS(1)), mass errors to theoretical [TBPH-Br+O](-) were 2.1 and 1.0 ppm for the two isomers, UHR-MS(2) spectra and NMR analysis; the structures of the two compounds were identified as hydroxylated TBPH with a hydroxyl group on the aromatic ring. Relatively great proportions of the two isomers of OH-TBPH were detected in two technical products, Firemaster 550 (FM-550; 0.1% and 6.2%, respectively) and Firemaster BZ 54 (BZ-54; 0.1% and 7.9%), compared to a commercial standard (0.4% and 0.9%). To simultaneously analyze OH-TBPH isomers and TBPH in samples of dust, a method based on LC-UHRMS was developed to quantify the two compounds, using negative and positive ion modes, respectively. The instrumental limit of detection for TBPH was 0.01 μg/L, which was 200-300 times better than traditional methods (2.5 μg/L) based on gas chromatography-mass spectrometry. The analytical method combined with a Florisil cleanup was successfully applied to analyze TBPH and OH-TBPH in 23 indoor dust samples from Saskatoon, Saskatchewan, Canada. Two OH-TBPH isomers, OH-TBPH1 and OH-TBPH2, were detected in 52% and 91% of dust samples, respectively. Concentrations of OH-TBPH2 (0.35 ± 1.0 ng/g) were 10-fold greater than those of OH-TBPH1 (0.04 ± 0.88 ng/g) in dust, which was similar to profiles in FM-550 and BZ-54. TBPH was also detected in 100% of dust samples with a mean concentration of 733 ± 0.87 ng/g. A significant (p < 0.001) log-linear relationship was observed between TBPH and OH-TBPH isomers, further supporting the hypothesis of a common source of emission. Relatively small proportions of OH-TBPH isomers were detected in dust (0.01% ± 0.67 OH-TBPH1 and 0.1% ± 0.60 OH-TBPH2), which were significantly less than those in technical products (p < 0.001). This result indicated different environmental behaviors of OH-TBPH and TBPH. Detection of isomers of OH-TBPH is important, since compounds with phenolic groups have often shown relatively greater toxicities than nonhydroxylated analogues. Further study is warranted to clarify the environmental behaviors and potential toxicities of OH-TBPH isomers.

Elucidating Molecular Structures of Nonalkylated and Short-Chain Alkyl (n &lt; 5, (CH2)n) Aromatic Compounds in Crude Oils by a Combination of Ion Mobility and Ultrahigh-Resolution Mass Spectrometries and Theoretical Collisional Cross-Section Calculations

Ultrahigh-resolution mass spectrometry has allowed the determination of elemental formulas of the compounds comprising crude oils. However, elucidating molecular structures remains an analytical challenge. Herein, we propose and demonstrate an approach combining ion mobility mass spectrometry (IM-MS), ultrahigh-resolution mass spectrometry, and theoretical collisional cross-section (CCS) calculations to determine the molecular structures of aromatic compounds found in crude oils. The approach is composed of three steps. First, chemical structures are suggested based on the elemental formulas determined from ultrahigh-resolution mass spectra. Second, theoretical CCS values are calculated based on these proposed structures. Third, the calculated CCS values of the proposed structures are compared with experimentally determined CCS values from IM-MS data to provide proposed structures. For proof of concept, 31 nonalkylated and short-chain alkyl (n < 5, (CH2)n) aromatic compounds commonly observed in crude oils were analyzed. Theoretical and experimental CCS values matched within a 5% RMS error. This approach was then used to propose structures of compounds in selected m/z regions of crude oil samples. Overall, the combination of ion mobility mass spectrometry, ultrahigh-resolution mass spectrometry, and theoretical calculations was shown to be a useful tool for elucidating chemical structures of compounds in complex mixtures.

Atmospheric organic matter in clouds: exact masses and molecular formula identification using ultrahigh-resolution FT-ICR mass spectrometry

Abstract. Clouds alter the composition of atmospheric aerosol by acting as a medium for interactions between gas- and particulate-phase substances. To determine the cloud water atmospheric organic matter (AOM) composition and study the cloud processing of aerosols, two samples of supercooled clouds were collected at the Storm Peak Laboratory near Steamboat Springs, Colorado (3220 m a.s.l.). Approximately 3000 molecular formulas were assigned to ultrahigh-resolution mass spectra of the samples after using a reversed-phase extraction procedure to isolate the AOM components from the cloud water. Nitrogen-containing compounds (CHNO compounds), sulfur-containing compounds (CHOS and CHNOS compounds) and other oxygen-containing compounds (CHO compounds) with molecular weights up to 700 Da were observed. Average oxygen-to-carbon ratios of ∼0.6 indicate a slightly more oxidized composition than most water-soluble organic carbon identified in aerosol studies, which may result from aqueous oxidation in the clouds. The AOM composition indicates significant influences from biogenic secondary organic aerosol (SOA) and residential wood combustion. We observed 60% of the cloud water CHO molecular formulas to be identical to SOA samples of α-pinene, β-pinene, d-limonene, and β-caryophyllene ozonolysis. CHNO compounds had the highest number frequency and relative abundances and are associated with residential wood combustion and NOx oxidation. Multiple nitrogen atoms in the assigned molecular formulas for the nighttime cloud sample composite were observed, indicating the significance of nitrate radical reactions on the AOM composition. Several CHOS and CHNOS compounds with reduced sulfur (in addition to the commonly observed oxidized sulfur-containing compounds) were also observed; however further investigation is needed to determine the origin of the reduced sulfur-containing compounds. Overall, the molecular composition determined using ultrahigh-resolution Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry provides an unambiguous identification of the cloud water organic anion composition in the Rocky Mountain area that could help to improve the understanding of aqueous-phase processes.

Influence of heteroatom pre-selection on the molecular formula assignment of soil organic matter components determined by ultrahigh resolution mass spectrometry

Soil organic matter (SOM) is involved in many important ecosystem processes. Ultrahigh resolution mass spectrometry has become a powerful technique in the chemical characterization of SOM, allowing assignment of elemental formulae for thousands of peaks resolved in a typical mass spectrum. We investigated how the addition of N, S, and P heteroatoms in the formula calculation stage of the mass spectra processing workflow affected the formula assignments of mass spectra peaks. Dissolved organic matter extracted from plant biomass and soil as well as the soil humic acid fraction was studied. We show that the addition of S and P into the molecular formula calculation increased peak assignments on average by 17.3 % and 10.7 %, respectively, over the assignments based on the CHON elements frequently reported by SOM researchers using ultrahigh resolution mass spectrometry. The organic matter chemical characteristics as represented by van Krevelen diagrams were appreciably affected by differences in the heteroatom pre-selection for the three organic matter samples investigated, especially so for the wheat-derived dissolved organic matter. These results show that inclusion of both S and P heteroatoms into the formula calculation step, which is not routinely done, is important to obtain a more chemically complete interpretation of the ultrahigh resolution mass spectra of SOM.

Dioxin Analysis by Gas Chromatography-Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (GC-FTICRMS)

The feasibility of utilizing a gas chromatograph-tandem quadrupole-Fourier transform ion cyclotron resonance mass spectrometer (GC-MS/MS-FTICRMS) to analyze chlorinated-dioxins/furans (CDDs/CDFs) and mixed halogenated dioxins/furans (HDDs/HDFs) was investigated by operating the system in the GC-FTICRMS mode. CDDs/CDFs and mixed HDDs/HDFs could be analyzed at 50,000 to 100,000 resolving power (RP) on the capillary gas chromatographic time scale. Initial experiments demonstrated that 1 pg of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 5 pg of 2-bromo-3,7,8-trichlorodibenzo-p-dioxin (BTrCDD) could be detected. The feasibility of utilizing an FTICRMS for screening of CDDs/CDFs, HDDs/HDFs and related compounds was also investigated by analyzing an extract from vegetation exposed to fall-out from an industrial fire. CDDs/CDFs, chlorinated pyrenes and chlorinated tetracenes could be detected from a Kendrick plot analysis of the ultrahigh resolution mass spectra. Mass accuracies were of the order of 0.5 ppm on standards with external mass calibration and 1 ppm on a sample with internal mass calibration.

Direct molecular evidence for the degradation and mobility of black carbon in soils from ultrahigh-resolution mass spectral analysis of dissolved organic matter from a fire-impacted forest soil

The molecular composition of water-soluble products generated by the natural degradation of charcoal particles over a period of 100 years in a temperate forest soil has been investigated by ultrahigh resolution mass spectrometry with electrospray ionization. The detectable products are condensed aromatic ring structures extensively substituted with oxygen-containing functional groups, indicating that oxidation and dissolution of charcoal black carbon occurs on a centennial timescale. Many of the same species are also detected within the dissolved organic matter (DOM) of the forest’s soil pore waters. We introduce the calculation of carbon normalized double bond equivalents (DBE/C) as a structural determinant for the empirical formulas obtained by mass spectral analysis. A threshold DBE/C value of 0.7 serves as a criterion for identifying species with condensed aromatic ring structures (CARS). A comparison with ultrahigh resolution mass spectra from previous studies shows that many of the CARS extracted directly from soil BC have the same mass (within 1 ppm) and empirical formulas as CARS detected in volcanic ash soil humic acid (HA) from Japan, and Amazonian Rio Negro DOM. The similarity of water-soluble condensed aromatics present within, and exported from fire-impacted soils of geographically and climatically disparate ecosystems indicates that the CARS reported herein are the molecular fingerprint of black carbon degradation in soils. Understanding the production mechanisms, reactivity, and fate of these molecular species should provide new insight to BC degradation and cycling. The soil charcoal particles at this site are infiltrated by filamentous microorganisms, suggesting that saprophytic fungi may be important to soil BC degradation processes.

Hydrogen-deficient molecules in natural riverine water samples—evidence for the existence of black carbon in DOM

Understanding the role of black carbon (BC) in the natural environment is very important because of the potential impacts of black carbon on human health, global carbon cycling, and pollutant transport. There has been circumstantial evidence for the existence of black carbon molecules in dissolved organic matter (DOM); however, direct evidence has been lacking. In this paper, the presence of black carbon-like material in DOM is demonstrated for the first time. Electrospray ionization (ESI) with ultra-high resolution mass spectrometric analyses of DOM samples reveals the existence of hydrogen-deficient molecules. The van Krevelen analysis of the ultra-high resolution mass spectra clearly differentiates black carbon-like material from the complex assemblage of other, relatively hydrogen-rich natural molecules and indicates that the hydrogen-deficient molecules in the DOM are from black carbon-like material. The observation of black carbon molecules in DOM suggests that BC may be degraded and included in the active carbon pools of the earth.

Kendrick mass defect spectrum: a compact visual analysis for ultrahigh-resolution broadband mass spectra.

At currently achievable Fourier transform ion cyclotron resonance broadband mass spectrometry resolving power (m/deltam50% > 350,000 for 200 < m/z < 1,000), it would be necessary to spread out a conventional mass spectrum over approximately 200 m in order to provide visual resolution of the most closely resolved peaks. Fortunately, there are natural gaps in a typical mass spectrum, spaced 1 Da apart, because virtually no commonly encountered elemental compositions yield masses at those values. Thus, it is possible to break a broadband mass spectrum into 1-Da segments, rotate each segment by 90 degrees, scale each segment according to its mass defect (i.e., difference between exact and nominal mass), and then compress the spacing between the segments to yield a compact display. For hydrocarbon systems, conversion from IUPAC mass to "Kendrick" mass (i.e., multiplying each mass by 14.00000/14.01565) further simplifies the display by rectilinearizing the peak patterns. The resulting display preserves not only the "coarse" spacings (e.g., approximately 1 Da between odd and even masses, corresponding to either even vs odd number of nitrogens or 12C(c) vs 12C(c-1)13C1 elemental compositions of the same molecule; approximately 2-Da separations, corresponding to a double bond or ring; approximately 14 Da separations, corresponding to one CH2 group) but also the "fine structure" (i.e., different mass defects for different elemental compositions) across each 1-Da segment. The method is illustrated for experimental electrospray ionization FTICR ultrahigh-resolution mass spectra of a petroleum crude oil. Several thousand elemental compositions may be resolved visually in a single one-page two-dimensional display, and various compound families-class (NnOoSs), type (Z in C(c)H2(c+z)NnOoSs), and alkylation series-may be identified visually as well.